1. Field of the Invention
The present invention is related to an organic electroluminescence element, which is disposed with an arbitrary emitting color element at random after doping a predetermined emissive material (dye) at a predetermined position in an emissive layer of organic electroluminescence that is driven by a low voltage and luminous, and a manufacturing method thereof.
2. Description of the Related Arts
Generally, an organic electroluminescence element, which emits light by itself and has an ability of high-speed response and is independent of a viewing angle and anticipates lower power consumption, is considered as a display of the next generation. An area color system that combines monochromatic color partially is practically applied to a display panel for an audio system installed in an automobile and a display in which colors of red (R), green (G) and blue (B) are patterned by the masked vacuum evaporation method is practically applied to a cellular phone. Combining displaying elements corresponding to colors of red (R), green (G) and blue (B) enables to display full-color, so that various studies for obtaining an organic electroluminescence element in high performance that is driven by low voltage and emits light in high intensity are performed. A typical structure of organic electroluminescence element is that a thin film layer composed of an organic material is laminated on a transparent substrate such as glass, which is coated with a transparent electrode such as indium-tin oxide (ITO), and a metal electrode such as an alloy of MgAg (magnesium-silver) is laminated over the thin film layer. With respect to an organic material of the thin film layer or emissive layer that lies between the transparent electrode and the metal electrode, materials having fluorescence such as from polymer material to small molecular material, metal complex, and further heavy metal complex that has phosphorescence and emits light in extremely high efficiency are widely used. A method of laminating such an organic material is selected out of a wet method such as a coating method and a dry method such as the vacuum evaporation method in accordance with an organic material. An organic layer or the emissive layer in an organic electroluminescence element is divided into two types. One is a single layer type that is composed of only one layer and the other is a laminated layer type, which is multi-layered by a plurality of different materials in accordance with functions such as polarity of injecting electric charge, mobility of transporting electric charge and light-emitting ability. Light emitted from the organic layer is conducted through a transparent electrode or a transparent substrate.
FIG. 11 is a cross sectional view of an organic electroluminescence element of the prior art. In FIG. 11, an organic electroluminescence element is composed of a transparent substrate 2 that is made by glass or like and coated with a transparent electrode 4 of indium-tin oxide (ITO) or like thereon, a hole transport layer 6 of aryl diamine compound, a emissive layer 8 of organic metal complex of tris (8-quinolinol) aluminum (Alq3) as an electron transporter and a metal electrode 10 of the alloy of magnesium-silver (MgAg alloy). They are laminated in order. When a certain voltage is applied across the transparent electrode 4 and the metal electrode 10, a hole is injected from the transparent electrode 4 of ITO and an electron is injected from the metal electrode 10 of MgAg alloy. The hole and the electron recombine together at a neighborhood of boundary of organic layer between the hole transport layer 6 and the emissive layer 8, and emit light xe2x80x9cLxe2x80x9d. The light xe2x80x9cLxe2x80x9d emitted from the emissive layer 8 is conducted to the outside of the organic electroluminescence element through the transparent electrode 4 and the transparent substrate 2. The emitted light is monochromatic light that depends on an emitting color of the emissive layer 8. In this case, the color of emitted light is green, which is caused by Alq3 mentioned above.
A so-called doping method is used for controlling chromaticity of a color of emitted light and increasing luminous intensity by mixing dye having a predetermined wavelength of emitted light in the emissive layer 8 and causing energy transfer from a host of the emissive layer to the dye. With respect to a material of the host of emissive layer, it is supposed to be necessary for the host material that emission spectrum of the host material has a wavelength within a same wavelength region as that of absorption spectrum of doped dye, or a shorter wavelength region than that of the absorption spectrum of the doped dye so as to overlap with the absorption spectrum of doped dye.
In order to display in full-color by conducting emitted light externally, it is essential to combine microscopic elements (sub-pixels) of each emitted light in colors of R, G and B into one pixel. Generally, a method such as the vacuum evaporation method and the coating method is used for manufacturing an organic electroluminescence element. However, it is hard to dispose elements in different colors of emitted light minutely. In a case of the vacuum evaporation method by using a small molecular material, for example, it is necessary for a deposition mask having a microscopic pixel shape to move, locate and face with each other accurately with keeping the mask so as to be apart from a pixel section and contact with a substrate closely. If a pixel area becomes more microscopic, increasing accuracy is required for mask producing technique and mechanism for locating and transferring, and it is resulted in decreasing productivity. Further, it is essential for a mask to be not only smaller in opening size but also thinner in thickness in accordance with a trend for higher definition. Therefore, handling of a mask such that bending or out of registration by heat causes positioning or replacing the mask becomes harder.
In a case of using a polymer material, a method of forming a microscopic pattern by coating each color emissive material on a pixel section through the ink-jet method is proposed. However, further improvement is required in accordance with a trend for higher definition such that an ink-jetting direction and an ink-jetting amount of droplet of each color emissive material is required for accuracy, ink-jetted droplet must be disposed in a predetermined position and a separator or bank of which surface is treated for decreasing surface energy is necessary for a substrate side to prevent the solution from breeding out from the predetermined position while drying.
Under these circumstances, following techniques are proposed for solving the above-mentioned problems so as to manufacture each of R (red), G (green) and B (blue) elements in high definition.
In order to emit white light, which covers a visible light range in a emissive layer as wide as possible, for example, a emissive layer in which plural kinds of fluorescent dye are diffused is formed. The emissive layer is referred to as a white emissive layer. The white emissive layer is combined with a color filter so as to produce any emitting color of R, G and B. Consequently, sub-pixels can be microscopically disposed by being combined with a color filter that is produced by the photolithography technique without disposing a emissive layer minutely.
Further, in a case of emitting white light, there has been provided a plurality of methods through the vacuum evaporation method such that laminating each of R, G and B layers and combining a B layer with a yellow emissive layer, which is in relation to complimentary color of B-color light, produces white light. However, a white-light emitting element having high efficiency and long life is hard to be realized in comparison with a monochromatic-light emitting element.
Furthermore, there existed another problem that utilization efficiency of emitted light decreases because a white-light emitting element is designated to be each color light-emitting element through a color filter.
More, a method of forming a blue emissive layer and a color converting layer, which converts blue light emitted from the blue emissive layer into green and red by the down-conversion of wavelength, has been proposed. However, there still existed room for further improvement such as efficiency of converting blue into red and converted chromaticity, in particular.
Moreover, in a case of patterning of polymer emissive material, the Japanese Patent Application Laid-open Publication No. 7-235378/1995 and the U.S. Pat. No. 5,895,692 (Apr. 20, 1999) disclose a method of dispersing dye into a polymer emissive layer by the infrared heating method, wherein a layer containing R, G and B fluorescent dye is formed on the surface of the polymer emissive layer by the ink-jet method or the screen printing method after the polymer emissive layer has been produced by the wet method such as the spin coating and dip coating methods. With respect to the screen printing method, forming a bank in an area other than an opening section is essential so as to dispose ejected ink accurately, and resulted in difficulty of manufacturing in accordance with advancing higher definition.
In addition thereto, with respect to a method of patterning fluorescent dye by heating, a method of sublimating and dispersing dye confronting with a emissive layer through a shadow mask from a layer of dye in high density to the emissive layer is disclosed in the publication: xe2x80x9cApplied Physics Lettersxe2x80x9d, vol. 74, No. 13, pp. 1913-1915 (1999). Another method of heating an ITO (indium tin oxide) lower electrode composed of a high density dye layer and a emissive layer confronting with each other is disclosed in the publication: xe2x80x9cJapanese Journal of Applied Physicsxe2x80x9d, vol. 38 Part 2, No. 10A, pp. L1143-L1145 (1999).
As mentioned above, the masking method is resulted in difficulty of producing pattern in high definition when making the pattern more microscopic as the same situation as the vacuum evaporation method. In the case of the method of heating by electrode, temperature difference between the electrode and its surrounding area is essential, so that the method is unsuitable for an element in high definition.
Accordingly, in consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide an organic color electroluminescence element, which is small in size, high in definition, high in performance and excellent in productivity, and to provide a manufacturing method of the organic color electroluminescence element by making use of characteristics of organic thin film electroluminescence.
In order to achieve the above object, the present invention provides, according to an aspect thereof, an organic electroluminescence element comprising: a plurality of first electrodes disposed on a substrate in matrix; a second electrode disposed with being confronted with each of the plurality of first electrodes; and a emissive layer formed between each of the plurality of first electrodes and the second electrode on each of the plurality of first electrodes, wherein the emissive layer is composed of a blue (B) emissive layer, a green (G) emissive layer and a red (R) emissive layer as a set of pixels, the organic electroluminescence element is further characterized in that the B emissive layer contains a B emissive material, the G emissive layer contains B and G emissive materials, and the R emissive layer contains B, G and R emissive materials.
According to another aspect of the present invention, there provided a manufacturing method of an organic electroluminescence element comprising steps of: forming a first electrode divided by a plurality of separators and disposed on a substrate in matrix; forming a blue (B) emissive layer on the first electrode by diffusing a B emissive material; obtaining a green (G) emissive layer adjacent to the B emissive layer after diffusing a G emissive material in a part of the B emissive layer; obtaining a red (R) emissive layer adjacent to the G emissive layer after diffusing a R emissive material in a part of the G emissive layer; and forming a second electrode on each of the R and G and B emissive layers.
According to further aspect of the present invention, there provided a manufacturing method of an organic electroluminescence element comprising at least a first electrode, a emissive layer and a second electrode on a substrate, the manufacturing method comprising steps of: forming a plurality of first electrodes on the substrate; forming at least either one of an electric charge injecting layer and an electric charge transporting layer on the plurality of first electrodes; forming a emissive layer on the plurality of first electrodes; forming at least either one of the electric charge injecting layer and the electric charge transporting layer on the emissive layer; and forming a second electrode on at least either one of the electric charge injecting layer and the electric charge transporting layer, the manufacturing method is further characterized in that emissive layers for a blue (B) color, a green (G) color and a red (R) color are formed in order during the step of forming a emissive layer.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.